The present invention relates generally to an exposure apparatus and method, and more particularly to an exposure apparatus and method that exposes an object, such as a single crystal substrate of a semiconductor wafer and a glass plate for a liquid crystal display (“LCD”). The present invention is suitable for a so-called immersion exposure apparatus that fills a space with liquid between a final surface of a projection optical system and a surface of an object, and exposes the object via the liquid.
Conventionally, the photolithography technology has employed a reduction projection exposure apparatus using a projection optical system to project a circuit pattern of a reticle (mask) onto a wafer, etc., in manufacturing fine semiconductor devices such as a semiconductor memory and a logic circuit.
The minimum critical dimension to be transferred by the projection exposure apparatus or resolution is proportionate to a wavelength of light used for exposure, and inversely proportionate to the numerical aperture (“NA”) of the projection optical system. The shorter the wavelength is, the better the resolution is. Along with recent demands for finer processing to the semiconductor devices, a shorter wavelength of ultraviolet light has been promoted from a KrF excimer laser (with a wavelength of approximately 248 nm) to an ArF excimer laser (with a wavelength of approximately 193 nm). Currently, the next generation light sources are being developed, such as an F2 laser (with a wavelength of approximately 157 nm) and extremely ultraviolet (“EUV”) light.
With this background, the immersion exposure has attracted attentions as a method that uses the ArF laser for more improved resolution. The immersion exposure fills a space with the liquid between the final lens surface of the projection optical system and the image surface of the wafer (or arranges the liquid as a medium at a wafer side of the projection optical system). The immersion exposure shortens the effective wavelength of the exposure light, enlarges the apparent NA of the projection optical system, and improves the resolution.
In the immersion exposure, there are proposed two methods for filling liquid between the final lens surface of the projection optical system and the wafer. The first method puts the final lens surface of the projection optical system and the wafer under the liquid in a sink. The second method is a local fill method that flows liquid in a space between the projection optical system and the wafer and creates a liquid film. An exposure apparatus using this method is proposed. See, for example, “Bruce Smith, Exterme-NA Water Immersion Lithography for 35–65 nm Technology, International Symposium on 157 nm Lithography 3–6 Sep. 2002, Belgium” and International Publication No. WO99/49504.
FIG. 8 is a schematic sectional view of a conventional immersion exposure apparatus. Referring to FIG. 8, the conventional exposure apparatus supplies a liquid 1600 between opposing surfaces of a final lens surface 1100 and a wafer 1200 through a liquid supply nozzle 1300 installed near an edge part of the final lens surface 1100. Then, the conventional exposure apparatus recovers the liquid 1600 through a liquid recovery nozzle 1400 installed opposite to the final lens surface 1100. Moreover, an air curtain 1500 is formed by spraying compressed air from the outside of the liquid supply nozzle 1300 and the liquid recovery nozzle 1400, and maintains the liquid 1600 between the final lens surface 1100 and the wafer 1200.
International Publication No. WO99/49504 does not disclose the air curtain. However, the composition of the liquid supply nozzle and the liquid recovery nozzle is the same as FIG. 8. International Publication No. WO99/49504 has disclosed adjustments of a supply amount and recovery amount of the liquid according to a moving velocity of the water.
It is important for the immersion exposure to keep the liquid away from air bubbles, because they scatter the exposure light and deteriorates the imaging performance. The air bubbles are likely to occur, when a solid contacts a liquid surface (interface) and liquids contact each other. Therefore, continuous supplies of the liquid can reduce mixtures of the air bubbles.
However, at the time of the initial filling or when the liquid surfaces of the liquid supplied from the liquid supply nozzle are separated although the liquid exists between the final lens surface and the wafer, the liquid surfaces contact each other and the air bubbles likely to occur. This results in the reduced imaging performance due to the generated air bubbles, and the decreased productivity of semiconductor device manufacture. Moreover, the air bubbles are likely to mix the liquid in the structure shown in FIG. 8, because this structure sprays the compressed air to the liquid surface (meniscus surface) with which the air bubbles are likely to mix.
In International Publication No. WO99/49504, it is possible to keep the air bubbles hard away from the liquid by controlling flow rates of the supply and recovery of the liquid at the time of the initial filling. Where the liquid surface of the liquid supplied between the final lens surface and the wafer separates from that of the liquid supplied from the liquid supply nozzle are separated, the air bubbles are likely to occur when the continuously supplied liquids' surfaces contact each other. Therefore, the supply flow rate must be lowered. This configuration decreases the throughput of the exposure apparatus, and the productivity of semiconductor device manufacture.